Preheat the oven to 375°F and grease or spray a 9in pie plate with non-stick spray.
Begin by making the pie crust. Beat room temperature butter and sugar together until just fluffy, about 90-120 seconds. Then add egg, milk and vanilla and mix until combined, scraping down sides of bowl as needed. Add sifted flour, baking powder and cinnamon and mix until dough ball forms. Press dough evenly into pie plate and up sides. Place in freezer for 10 min. Then bake for 12-13 minutes until just golden brown on edges.
While the pie crust is chilling, peel the RubyFrost apples and dice into 1/2 inch pieces. Discard cores. Then put the pie crust into oven.
While the pie crust is baking, continue making the filling. Melt the butter then whisk in the cornstarch, flour and cinnamon. In a large bowl, mix the melted butter mixture with apples and lemon juice. Set aside. Check on pie crust and remove from oven when just barely golden brown on edges.
Next, make the crumble topping by whisking together the flour, brown sugar and cinnamon. Then add the melted butter and stir with fork until crumbly pieces form.
Assemble pie by adding apple filling, mounding in the middle. Then pack crumble topping onto the filling, sprinkling the last few pieces of topping on top of the packed topping. Place pie plate onto baking sheet to catch any drips. Lay a piece of foil over top and bake for 40 minutes at 350°F. After 40 minutes, remove foil and continue baking for an additional 35-40 minutes until filling is bubbling. Let pie cool for two hours to let filling set. Then slice and enjoy!